Atmosphere - Chemical

The atmosphere is made of gases (78% nitrogen, 21% oxygen and smaller amounts of other gases, such as carbon dioxide), and water vapor. It extends to nearly 500km above the earth's surface.

Quick facts

Despite the terms

'air' and 'oxygen' often being used synonymously, oxygen only makes up 21% of the gas in the atmosphere[1]

Chemical components in the atmosphere

The atmosphere supports life by supplying chemicals for life (such as oxygen), protects the earth from solar radiation and cycles heat and water through the climate system.

The main chemical components in the atmosphere are:

• Carbon dioxide: Carbon dioxide, CO₂ forms 0.0407%, or 412 parts per million, of the atmosphere and is increasing. It has increased 47% since the Industrial Age. Carbon dioxide is a greenhouse gas, which traps earth's radiant heat and stops it all radiating into space. Carbon dioxide is one of many greenhouse gases that keeps earth's climate warm[3].
• Nitrogen compounds: Nitrogen compounds form 78.1% of the atmosphere[2]. In its gaseous form, nitrogen is colourless, odourless and is generally considered as inert. Nitrogen compounds found in the atmosphere include Nitrogen gas (N₂) (dinitrogen), nitrogen dioxide (NO₂) and Nitrous oxide gas (N₂O). The many compounds of nitrogen are listed on the Chemical forms page. Nitrous oxide gas is a greenhouse gas.
• Oxygen/Ozone: Oxygen, O₂, forms 20.95% of the atmosphere[1]. Oxygen is necessary for most forms of animal life, as it plays a critical role in respiration. It is also necessary for combustion (burning)[4][1]. Oxygen is generated from plants during photosynthesis. Oxygen can also form a molecule of three atoms in the atmosphere, which is known as ozone (O₃). Ozone blocks most of the harmful UV radiation from the sun, while ozone in the troposphere (the lowest atmospheric layer) is a hazardous pollutant.

The atmosphere of primordial earth contained no oxygen. For over 3 billion years, the oxygen produced by photosynthesis reacted with iron dissolved in the oceans generating significant quantities of iron oxide and turning the world’s oceans rusty red. These remain today as rich iron ore deposits where these ancient oceans occurred in places like the Pilbara in Western Australia.

Eventually the iron and other reducing minerals in the oceans were exhausted by the oxygen produced by early life and first the oceans, then the atmosphere began to oxygenate. The reactivity of oxygen had a significant impact on lifeforms generally unaccustomed to it, leading to the world’s first mass extinction event. The reduction of the existing dominant life opened opportunities for diversification, and the presence of oxygen lead to evolution of the first multicellular lifeforms. This lead to the greatest biological diversification of all time – the Cambrian explosion. This is where ancestral forms of all the major phyla evolved.

References

1. ^ a b c Hamblin, WK & Christiansen, EH (2001), Earth's dynamic systems, Prentice Hall, Upper Saddle River, NJ.
2. ^ Kotz, JC, Treichel, P, Townsend, JR & Treichel, DA (2019), Chemistry & chemical reactivity, p. 1187, Cengage Learning, Boston, MA.
3. ^ Luo, Y, Huang, L, Lei, X, Yu, X, Liu, C, Jiang, L, Sun, Y, Cheng, M, Gan, J, Zhang, Y, Zhou, G, Liu, S, Lian, J & Huang, H (May 2022), 'Light availability regulated by particulate organic matter affects coral assemblages on a turbid fringing reef', Marine Environmental Research. [online], vol. 177, p. 105613. Available at: https://linkinghub.elsevier.com/retrieve/pii/S0141113622000587 [Accessed 6 September 2023].
4. ^ National Oceanic & Atmospheric Administration (NOAA) (2023), The Atmosphere. [online] Available at: https://www.noaa.gov/jetstream/atmosphere.

Last updated: 15 September 2023